(1) Field of the Invention
The invention relates to the fabrication of integrated circuit devices, and more particularly, to a method of removing water spots induced by a hydrofluoric acid etch in the manufacture of integrated circuits.
(2) Description of the Prior Art
In the manufacture of integrated circuits the presence of tiny impurities on the surface of a wafer may cause failures in devices built upon or under these impurities. Referring to FIG. 1A, there are illustrated droplets of de-ionized water 2 on the surface 1 of a wafer. After a hydrofluoric acid etch a wafer is typically rinsed in de-ionized water. These droplets are formed into water tracks during spin-drying, indicated by arrow 4. Referring to FIG. 1B, the water droplets are spun off in the drying process, but impurities 2 remain on the surface of the wafer 1 in the form of water tracks 3. These impurities contain oxygen and can be seen through a microscope to be on and in the surface of the wafer.
Native oxide layers which are formed when the silicon substrate of an integrated circuit is exposed to the air may also cause problems. Since a native oxide layer is formed in an uncontrolled manner, the thickness of the layer may not be uniform throughout. In particular, in the case of buried contacts, the native oxide layer above a planned buried contact may act as a diffusion barrier when ions are implanted to form the buried contact. It is desirable to control the formation of the native oxide so that its thickness is both uniform and known.
Japanese Patent JA 2-307277 to Ito describes an etching and cleaning process followed by a controlled oxidation of the substrate to produce a uniform thickness oxide layer. This controlled oxidation is a two-hour process.